The interest in harnessing renewable sources of energy for space heating in residential applications has increased in recent decades due in part to their cost benefits and an increase in environmental awareness. The proposed system uses shallow ground as an energy reservoir; able to absorb heat during the summer and release it during the winter respectively. This paper presents by means of a mathematical model an analysis of such a system using real temperature profiles and compares them to idealized fitted functions. A validated two-dimensional multiphase model describing mass, momentum, turbulence and conjugate heat transfer between the bayonet tube and the ground is used to compare the effects of using a simplified fitted function to represent the ambient temperature with that of hourly temperature readings from a weather monitoring station. The results indicate that the strong random nature of the temperature variations complicates the analysis. It is shown that fitted functions can over predict the overall performance of the system, however under-predict the performance on the short term due in part to cold snaps, heat waves and variations in temperatures. While the benefits and capabilities of the system under real loads show the potential of the system, work on thermal buffering or real-time intelligent control systems for quality control will be necessary to maintain constant temperature for thermal comfort and optimum energy extraction.